Purification of alkyl sulphates



Patented Nov. 7, 1939 more STATES eA'rsuT creme PURIFICATION OF ALKYL SULPHATES No Drawing.

Application November 29, 1935,

Serial No. 52,199

10 Claims.

This invention relates to an improved method for preparing detergents, and more particularly to the preparation of detergents of high purity and effectiveness from crude alkyl sulphates and similar detergent compositions.

The use as detergents of the alkali metal salts of the sulphuric derivatives of the higher fatty alcohols and of similar alkyl reagents, such as sodium lauryl sulphate, is known. These detergents are usually produced by treating an alkyl reagent, such as an alcohol having a chain of about 8 to 25 carbon atoms,- with a strong sulphuric reagent, usually sulphuric acid and its derivatives, and then neutralizing the reaction product with a suitable base to form water-soluble salts of the alkyl sulphates. A substantial quantity of unreacted sulphuric or similar acid remains in the reaction mixture even after careful washing, and this, on neutralization, forms inorganic salts which remain in the detergent product. For many purposes it is desirable that the alkyl sulphate salt, or soap, as it is conveniently classifled on account of its detergent properties, should be substantially free of inorganic salts. It has 5 been found, however, that these inorganic salts are extremely diflicult to separate from the crude soaps.

It is an object of this invention to prepare a substantially salt-free alkyi sulphate soap. It 9 found that the inorganic salts can be precipitated if the soap composition is dissolved in an organic solvent and the solution is then rendered substantially anhydrous. It is a further object of this invention to accomplish this 5 dehydration by an improved method by which overheating and degradation of the soaps are avoided.

The following example is presented to illustrate a suitable method for conducting the present invention, and is not to be construed in any way as a limitation thereof:

Example I Parafiin wax was subjected to limited oxidation 3 with air for the preparation of fatty acids. The resulting acids were separated from the crude oxidation product by saponification. The crude unsaponified fraction was extracted with aqueous methyl alcohol (93% strength) and the oxyorganic fractions thus concentrated in the extract were hydrogenated to reduce ketones and aldehydes to alcohols. Hydrogenation catalysts, such as nickel, may be used for this treatment with hydrogen under suitable conditions of tem- 5 peratures and pressures, for example, at temperatures of ISO-300 C. or higher, and pressures of 30-150 atmospheres, to effect the desired reduction. The hydrogenated product consisted largely of secondary and tertiary aliphatic alcohols of about 8 to 25 carbon atoms. ,6

This purified mixture of alcohols may be sulphat-ed in any suitable manner, using either the entire mixture or fractions thereof containing one or more alcohols, either isomers or members of a homologous series, or both. For example, 10 improved detergents are obtained by using a mixture containing alcohols having a chain of 16 to 18 carbon atoms, or narrower fractions thereof, and improved sudsing agents from alcohols having a chain of 10 to 14 carbon atoms. One suitable method is to add the alcohol slowly with stirring to a precooled mixture of anhydrous chlorsulphonic acid and ether with cooling to maintain a reaction temperature of about G-5 C.

The cold reaction mixture of sulphated alcohols 20 prepared as above was neutralized by adding it slowly to an aqueous solution containing a slight excess of caustic soda, with stirring and cooling to maintain a temperature below about C. during the neutralization. 25

The neutralized mixture was extracted with a light petroleum naphtha, such as petroleum ether, to remove unsulphated material, an upper layer of naphtha solution being separated from a lower layer of aqueous soap solution. This ex traction may be repeated several times as desired, or maybe operated with countercurrent flow of naphtha and soap solution.

One volume of the resulting aqueous soap solution, substantially free of unsulphated organic material, was then evaporated on a steam bath to a syrupy paste. Vacuum evaporation may be used if the soap is particularly sensitive to elevated temperatures, as is usually the case when any substantial amount of dialkyl sulphates are present, but with soaps of the type produced above, a careful heating at atmospheric pressure i satisfactory.

One volume of isopropyl alcohol (98% strength) was then mixed thoroughly with this paste, and the mixture was heated as before to evaporate about half of the added alcohol. The alcohol forms a constant boiling mixture with the water present in the paste, and this water is largely removed with the alcohol vapors. The inorganic salts are thereupon precipitated, and may be separated from the soap solution by any suitable means, such as filtration, sedimentation, or centrifugal separation. A convenient method is to add additional isopropyl alcohol (98% strength) to reduce the viscosity of the soap solution, and then to filter out the precipitated inorganic salts. The filter cake was washed with alcohol to recover any soap therein, and the combined filtrates were reduced to a paste by evapo ration on a steam bath and then to dryness in a vacuum oven. There was thus obtained a highly effective detergent or soap composition which contained only 0.6% of inorganic salts and 1.6% of water.

In place of the isopropyl alcohol shown in the above example, substantially any organic solvent may be used which is vaporizable at a temperature below that at which the soap decomposes, and which is capable of forming a constant-boiling mixture with water. Solvents boiling below C. are preferred, but higher boiling solvents may also be used, in which case the distillation is preferably conducted under vacuum. Examples of suitable solvents are the lower allphatic alcohols, ethers, and ketones.

The invention is also applicable to the treatment of other detergents and wetting agents, including the salts of strong mineral acid derivatives, particularly of strong polybasic mineral acids, such as sulfuric and phosphoric acids, of fatty alcohols, of alcohols obtained by hydrogenating natural fats and fatty acids and oxidized wax acids of similar molecular weight range, and of olefins of 8 to 25 carbon atoms, such as those obtained by cracking high molecular weight parafiin and highly parafinic oils, especially parafiin wax and petrolatum.

This invention is not to be limited to any explanations or examples, all of which are presented herein solely for purpose of illustration, but is limited only by the following claims, in which it is desired to claim all novelty insofar as the prior art permits.

We claim:

1. Process for separating inorganic salts from crude alkyl sulphates containing same and water, comprising adding a substantially anhydrous water-soluble volatile organic liquid, capable of forming a constant boiling mixture with water and vaporizable at a temperature below that at which said alkyl sulphates decompose, to the said crude alkyl sulphates, evaporating a substantial portion of said added organic liquid by heating, whereby the water content of the remaining alkyl sulphate composition is reduced and inorganic salts are precipitated therefrom, separating the precipitated inorganic salts and recovering an alkyl sulphate of increased purity.

2. Process according to claim 1, in which said added organic liquid is an aliphatic alcohol.

3. Process according to claim 1, in which said added organic liquid is isopropyl alcohol.

4. Process according to claim 1, in which said precipitated inorganic salts are separated from the alkyl sulphate composition by adding a substantially anhydrous organic solvent for said alkyl sulphates to said composition to reduce its viscosity, and filtering out said salts.

5. Process for separating inorganic salts from crude alkyl sulphates containing same and water, comprising drying the mixture of said components to a viscous mass containing less than about 50% of water, adding about 1 to 3 volumes of isopropyl alcohol of about 98% strength to the partially dried mixture, evaporating about half of the added alcohol, and separating the resulting precipitated inorganic salts from the remaining solution.

6. Process for separating inorganic salts from crude alkyl sulphates containing same and water, comprising drying the mixture of said components to a viscous mass containing less than about 50% of water, adding about 1 to 3 volumes of isopropyl alcohol of about 98% strength to the partially dried mixture, evaporating about half of the added alcohol, reducing the viscosity of the resulting mixture by adding additional isopropyl alcohol, filtering the diluted mixture to remove precipitated inorganic salts therefrom, and evaporating the filtered solution substantially to dryness to recover substantially anhydrous, salt-free, purified alkyl sulphates.

'7. Process according to claim 6, in which said crude alkyl sulphates are prepared by reaction of 1 an alkyl reagent selected from the group consisting of alcohols and olefins with a strong sulphuric reagent, followed by neutralization to form salts.

8. Process according to claim 6, in which said crude alkyl sulphates are prepared from a crude mixture of alcohols, obtained by limited oxidation of paraflin hydrocarbons, by treatment with a strong sulphuric reagent, followed by neutralization to form salts.

9. Process according to claim 6, in which said crude alkyl sulphates contain about 8 to 25 carbon atoms in the alkyl group.

10. Process for removing from alkyl sulphates prepared by reacting alcohols of about 8 to 25 carbon atoms derived from the limited oxidation of wax with strong sulphuric acid and neutralizing the reaction product, the icy-product, inorganic salts, comprising adding a sufficient quantity of isopropyl alcohol to dissolve the alkyl sulphates and the occluded water containing dissolved inorganic salts, followed by partial evaporation, at a temperature below that at which said alkyl sulphates decompose, of the azeotropic mixture of alcohol and water sufiicient to maintain the alkyl sulphates in alcohol solution and to precipitate the inorganic salts, followed by filtration of the inorganic salt precipitate.

EGI V. FASCE. EMILE C. ROLFS, JR. 

